On the ambiguity of the image reconstruction problem

The well-known problem of image reconstruction from its spectrum modulus has been studied for a discretely defined function. An approach has been developed, allowing for the study of two-dimensional brightness distributions. It is shown that the retrieval ambiguity represents a lesser problem in the two-dimensional case     

Single-shot dynamics of pulses from a gas-filled hollow fiber

We present measurements of the performance characteristics of few-cycle laser pulses generated by propagation through a gas-filled hollow fiber. The pulses going into the fiber and the compressed pulses after the fiber were simultaneously fully characterized shot-by-shot by using two kHz SPIDER setups and kHz pulse energy measurements. Output-pulse properties were found to be exceptionally stable and pulse characteristics relevant for non-linear applications like high-harmonic generation are discussed. PACS 42.65.Re; 42.65.Ky; 42.65.Sf; 42.65.Jx     

Untersuchung von Wasser

Ohne Zusammenfassung     

Development and validation of a simple and isocratic reversed‐phase HPLC method for the determination of rilpivirine from tablets,nanoparticles and HeLa cell lysates

In the present investigation, a simple and isocratic HPLC‐UV method was developed and validated for determination of rilpivirine (RPV) from dosage forms (tablets and nanoparticles) and biological matrices like HeLa cell lysates. The separation and analysis of RPV was carried out under isocratic conditions using (a) a Gemini reversed‐phase C₁₈ column (5 µm; 4.6 × 150 mm) maintained at 35°C, (b) a mobile phase consisting of a mixture of acetonitrile and 25 m m potassium dihydrogen phosphate (in the ratio 50:50 v/v) at a flow rate of 0.6 mL/min and (c) atazanavir as an internal standard. The total run time was 17 min and the analysis of RPV and internal standard was carried out at 290 nm. The method was found to be linear (r² value > 0.998), specific, accurate and precise over the concentration range of 0.025–2 µg/mL. The lower limit of quantification was 0.025 µg/mL, the limit of detection was 0.008 µg/mL and the recovery of RPV was >90%. The stability of the RPV analytical method was confirmed at various conditions such as room temperature (24 h), ?20°C (7 days), three freeze?thaw cycles and storage in an autosampler (4°C for 48 h). The method was successfully applied for the determination of RPV from conventional dosage forms like tablets, from polymeric nanoparticles and from biological matrices like HeLa cell lysates. Copyright © 2014 John Wiley & Sons, Ltd.     

Modeling the evolution of stress due to differential shrinkage in powder-processed functionally graded metal–ceramic composites during pressureless sintering

Pressureless sintering of powder-processed functionally graded materials is being pursued to economically produce metal–ceramic composites for a variety of high-temperature (e.g., thermal protection) and energy-absorbing (e.g., armor) applications. During sintering, differential shrinkage induces stresses that can compromise the integrity of the components. Because the strength evolves as the component is sintered, it is important to model how the evolution of the differential shrinkage governs the stress distribution in the component in order to determine when the strength will be exceeded and cracking initiated. In this investigation, a model is proposed that describes the processing/microstructure/property/performance relationship in pressurelessly sintered functionally graded plates and rods. This model can be used to determine appropriate shrinkage rates and gradient architectures for a given component geometry that will prevent the component from cracking during pressureless sintering by balancing the evolution of strength, which is assumed to be a power law function of the porosity, with the evolution of stress. To develop this model, the powder mixture is considered as a three-phase material consisting of voids, metal particles, and ceramic particles. A micromechanical thermal elastic–viscoplastic constitutive model is then proposed to describe the thermomechanical behavior of the composite microstructure. The subsequent evolution of the thermomechanical properties of the matrix material during sintering is assumed to obey a power law relationship with the level of porosity, which is directly related to the shrinkage strain, and was refined to account for the evolving interparticle cohesion of the matrix phase due to sintering. These thermomechanical properties are incorporated into a 2-D thermomechanical finite element analysis to predict the stress distributions and distortions that arise from the evolution of differential shrinkage during the pressureless sintering process. Differential shrinkage results were verified quantitatively through comparison with the shape profile for a pressurelessly sintered functionally graded nickel–alumina composite plate with a cylindrical geometry, and the stress distribution results verified from qualitative observations of the absence or presence of cracking as well as the location in specimens with different gradient architectures. The cracking was mitigated using a reverse gradient at one end of the specimen, and the resulting distortions associated with the shape profile were determined to be no more than 15% reduced from the predictions. The effects of geometry were also studied out-of-plane by transforming the plate into a rod through an increase in thickness, while in-plane effects were studied by comparing the results from the cylindrical specimen with a specimen that has a square cross-sectional geometry. By transforming from a plate to a rod geometry, the stress no longer exceeds critical levels and cracks do not form. The results from the in-plane geometric study indicated that critical stresses were reached in the square geometry at temperatures 100 °C less than in the cylindrical geometry. Additionally, the location of primary cracking was shifted towards the metal-rich end of the specimen, while the stress distribution associated with this shift and the lower temperature for the critical stress resulted in secondary cracking.     

Grid Method for Microscale Discontinuous Deformation Measurement

The objective of this paper is to explore both grid method and Digital Image Correlation (DIC) technique for microscale and discontinuous displacement measurements, such as those associated with crack tips. First, the principle of the grid method is revisited. The grid method and DIC technique are then applied to computer generated images to calculate the displacement field around crack tips. Finally, the grid method is applied to actual experimental images of fracture tests which are conducted inside a Scanning Electron Microscope (SEM) chamber. A new technique is developed to generate microscale pattern that is suitable for both grid method and DIC technique. The displacement fields calculated from grid method are compared with those from DIC technique to identify the strengths and weaknesses of each technique for the microscale and discontinuous displacement measurements. It has been determined that grid method can obtain data closer to the discontinuity than DIC; however, DIC produces smoother displacement fields at the far field. Using this new pattern generation technique, both grid method and DIC technique can be applied to the fracture test at the microscale to complement with each other to achieve the best experiment results.